Fungal wilt diseases

Soil fungi that affect the water-carrying parts of plants cause wilt diseases that can affect a wide range of vegetables, grains, and ornamentals. Fruit trees can also be affected.
Wilt diseases are commonly caused by not practicing a proper crop rotation. Adding organic matter to soil helps to limit soil-borne diseases because the beneficial fungi in organic matter out compete the pathogens. Avoid using glyphosate because it has been shown to affect the microorganisms in soil that assist in keeping diseases under control.
To find out which fungus is affecting your plants, pull out (if possible) one of the affected plants and cut open the stem near the roots.
If it’s Fusarium wilt, the inside of the stem (in most plants) will be pink to reddish brown. In beans, the inside of the stem will be dark brown with reddish roots. According to research recently published by the US Department of Agriculture, Fusarium diseases are becoming a serious problem in GM crops that have been engineered to be glyphosate-resistant. The research found that glyphosate exuding from the roots of this type of GM crops stimulates Fusarium fungi in soil. In wheat, these fungi cause Fusarium Head Blight. Fusarium produces several toxins in plants that are not destroyed by cooking. These become a health problem when present in large quantities. One type causes vomiting. Another type causes cancer and birth defects, while a third type of toxin is lethal. It is important to act to prevent the establishment of Fusarium in garden and agricultural soils.
If it’s Verticillium wilt, the outside of the stem appears normal but the inside of the stem will be dark brown to black. This disease is more common where drainage is poor. Improve drainage and control weeds. Give any unaffected plants in the bed a drink of seaweed extract tea as potassium and trace elements in this tea assist in building resistance to disease.
Remove all weeds and affected plants and burn them or dispose of them in a sealed plastic bag. Do this carefully, as spores can be spread by shoes, and gardening tools. Wear rubber boots and wash them and all tools after working in infected soil. Then dry these in direct sunlight.
When soil temperature is 14° C. or higher, grow a green manure crop of bio-fumigants such as Green Harvest’s BQ Mulch, yellow mustard, or radish. The peppery members of the Brassica family produce good quantities of glycosinolate that breaks down in wet soil to produce a gas that is effective against fungal pathogens and nematodes. Slash the green manure before it flowers, and hoe it into the topsoil. Then water the bed and cover it thickly with mulch.
Recent Spanish research has shown that, during summer, solarization is effective in treating these diseases. Place clear plastic sheets over irrigated beds and leave them in position for a minimum of 2 months.
Then grow a green manure crop of corn or maize and slash it when it is knee high and dig it into the topsoil. Wilt diseases are more common where soil is low in broken down or decomposed organic matter, and bio-fumigation will also affect beneficial mycorrhiza fungi in soil. Replacement of organic matter through green manures and as much compost as you can spare will encourage the re-establishment of mycorrhiza and other beneficial fungi and bacteria that can control soil pathogens when organic cultivation methods are used.
You will also need to practice a long crop rotation for different plant families until your soil is free of disease.

Wilt diseases

This post has been revised due to recent research. Click here.

Broad beans and peas

If you live in a frost area, make a note of when you sow peas, sweet peas or broad beans and when they start to flower. The foliage of these legumes is frost hardy, but the flowers are not. Yet, they do not crop well when temperatures are too warm. Peas can take from 7 to 10 weeks to produce flowers, and broad beans can take from 7 to 13 weeks to produce flowers, depending on local temperatures. Sowing too early or too late for local conditions can result in a disappointing crop. As a general rule where frosts occur, do not sow seed until 10 weeks before the usual last frosts in your area. If you have unusually late frosts, you can protect your plants with a temporary plastic canopy, if a frost is predicted.
It is too late to grow broad beans as a crop in warmer areas, but they can be sown in all areas as a green manure crop where you intend to sow tomatoes next spring. Broad beans inhibit the growth of fusarium wilt – a fungal soil disease that can affect a wide range of plants, including tomatoes. If grown as a green manure, the plants are slashed when knee high. Broad bean seed sold for green manures may be called fava, or faba, bean.
Peas, broad beans (and sweet peas) like a humus-rich soil with a pH of around 6.5. They will need an application of complete organic fertiliser (see post on Fixing nitrogen). Legumes also need the presence of molybdenum and cobalt in soil for good growth, and an application of seaweed extract tea to the bed before sowing, will ensure these trace elements are available.
Try to avoid periods of heavy rain when sowing legumes because they can rot before germinating in cold conditions. Having said that, we had a 98% germination rate for our peas that endured a week of heavy rain after sowing in a raised bed. The seed had been saved from last year’s crop and had not been treated with anything. I am at a loss to understand why major seed manufacturers feel the need to coat their legume seeds with toxic fungicides.